The best place to get sensors that work well with the eBox and Windows Embedded CE, is here. Development is supported in both C/C++ and .NET CF, and Phidgets offers a number of sensor types. The Sensor modules connect to the USB ports on the eBox, and if you need a number of sensors beyond the number of USB ports available, then you can always install a hub. A powered hub is required by certain Phidgets boards.
You can find other sensor platforms that connect to the RS-232 port on the eBox, rather than the USB ports. One that I am familar with is the Serializer sold by the RoboticConnection. The Serializer board provides an amazing array of I/O types all in one board, including GPIO, A2D, I2C, PWM, DC Motor Driver. It also offers .NET CF and C/C++ library support. You will still need to buy the actual sensor devices, but this board will give you the ability to connect to just about any interface required by the sensor hardware.
James Y. Wilson
Microsoft Embedded MVP
http://www.learningce.com
Fortudine Vincimus!